Practice makes not everything perfect. Just ask executive producer Ken Ehrlich, who despite meticulous rehearsals has had to adjust on the fly many times.

Frank Ocean cut a sharp figure in crisp jeans, a butterscotch tuxedo jacket and his signature multicolored headband while rehearsing at Staples Center for the Grammy Awards ceremony.

But as the R&B singer conferred with Grammy executive producer Ken Ehrlich following a run-through of his performance Thursday, another wardrobe item came into view: a wrist splint on Ocean's left arm. It was the result, presumably, of his alleged brawl last month with Chris Brown in the parking lot of a West Hollywood recording studio.

"Could we get a camera angle where it doesn't make my eyes look like they're closed all the time?" Ocean asked Ehrlich, the two men watching a playback on a bank of monitors. Ehrlich suggested the singer switch his microphone from his right hand to his left. Ocean silently raised the arm in question, his facial expression saying it all: Not happening.

The splint was a reminder that even in this most stage-managed of awards shows — a three-hour extravaganza, set to air Sunday night on CBS, featuring nearly two dozen musical performances — the real world can still intrude.

Last year reality imposed itself on the Grammys in unforgettable fashion, with the death of Whitney Houston just 24 hours before the ceremony was set to begin. The pop diva was found dead Feb. 11 in a room at the Beverly Hilton Hotel, where her longtime mentor Clive Davis throws his annual pre-Grammy gala. (The party on Saturday is expected to include an all-star tribute to Houston.)

But Ehrlich, a three-decade veteran of the Grammy Awards, is accustomed to the unexpected.

In 2009 the show was forced to replace Brown and Rihanna after he beat her badly during a Grammy weekend altercation. And in 1998 tenor Luciano Pavarotti bowed out minutes before showtime because of illness.

"I ran upstairs to Aretha [Franklin]'s dressing room," said Ehrlich. "I remembered she had sung 'Nessun Dorma' the night before at the [annual pre-Grammy] MusiCares show. I asked her if she would sing it again tonight."

It became one of the most memorable Grammy performances ever.

This year, a possible rematch between Ocean and Brown — both singers are nominated in the urban contemporary album category — isn't the only source of potential drama. The production is expected to reach an audience in the tens of millions, and those viewers will also be watching to see what happens between Brown and Rihanna. On Wednesday she accompanied him to an L.A. court hearing stemming from his assault on her four years ago.

But there's another potential wild card in this year's telecast: the proliferation of youthful, relatively untested acts up for nominations in top categories.

Can bands such as the Lumineers and Fun. pull off compelling performances and attract a wide audience? Even the nominees in the album of the year category — Ocean, the Black Keys, Jack White, Mumford & Sons and Fun. — are far from the usual fare of blockbuster pop acts and familiar heritage artists.

Though Rihanna isn't up for a major award this year, she is performing on the awards show — twice. Thursday she was wearing sweat pants and a letterman jacket, her hair tucked beneath a baseball cap, as the superstar pulled double duty at rehearsals, taking part first in a group performance with Bruno Mars, Sting and several of Bob Marley's sons.

The reggae-inspired crew ran through a spirited medley of the Police's "Walking on the Moon" and "Locked Out of Heaven" by Mars, who ceded a verse to Sting in winking acknowledgment of his song's strong Police vibe.

Mars, Ehrlich explained, initially wanted to take a year off the Grammy Awards. (The pop singer performed last year.) So the producer got to work. "I called Sting's manager, then I called Rihanna's people and then came back to Bruno and said, 'Here's what we've got,'" Ehrlich recalled. Mars took the bait.

Rihanna also ran through her ballad "Stay" on Thursday, and while she waited for cameras to move into place, her band launched into an impromptu rendition of Radiohead's "Everything in Its Right Place" — an indication of the eclectic musical mix Grammy producers are aiming for on Sunday's show.

Others artists set to perform at Staples Center, where streets around the venue have been blocked off in preparation for the celebrity tidal wave, include Taylor Swift, Justin Timberlake, the Black Keys, Kelly Clarkson, Carrie Underwood and Alicia Keys. A tribute to the late Levon Helm is also planned featuring Zac Brown, Mumford & Sons and Mavis Staples.

LL Cool J, who turned up Thursday evening trading jokes with Ehrlich and other Grammy organizers, will serve as host. He'll share the stage with presenters such as Beyoncé, Katy Perry and Jennifer Lopez.